The AFQT score is the overall score that is used to determine whether or not one is qualified to join a particular branch of the military. Each of the services have established a minimum score for their particular service.
The AFQT score is a "percentile," not a "percent correct." In 1980, a study, known as the "Profile of American Youth," was conducted by the Department of Defense in cooperation with the Department of Labor. DOD administered the ASVAB to a total of 11,914 individuals, ranging in age from 16 to 23, from July to October 1980. The purpose of the Profile of American Youth was to obtain data on the vocational aptitudes of current youth and to establish current national norms for the ASVAB.
The AFQT score is the "percentile" of how the applicant scores compared to the 1980 "test group." So, if an individual has an AFQT score of 50, that does not mean he/she got 50 percent of the answers correct. It means he/she scored better than 50 percent of the individuals who took the test in the above mentioned study.
However, comparing scores taken by applicants today to a group who took the test almost 25 years ago is not very realistic.
Over the past 24 years, aptitude levels in the United States have increased. Scores on educational achievement tests such as the National Assessment of Educational Progress (NAEP) are up; high school and college attendance rates have increased; youth demographics have shifted; and the country has experienced an explosion in technology development and application. Consequently, the 1980 norms are no longer representative of American youth.
Therefore, the Department of Defense has "re-normed" the ASVAB, using the 1997 Profile of American Youth, a national probability sample of 18 to 23 year olds who took the ASVAB in 1997. The change (new scoring) is effective for any ASVAB test given after July 1, 2004. Those who took the test prior to July 1 are scored on the old system, and these scores remain valid (ASVAB scores are valid for two years).
From my observations so far, the scoring difference does not appear to be significant -- a few points, at best. In other words, someone who scored an 89 under the old "norming" would probably have a score of around 85 or so under the new "norming."
So far, the Coast Guard is the only service which has announced any change in minimum ASVAB score requirements. Effective July 1, the Coast Guard changed their minimum score requirement from 40 to 36. The Air Force, which has the same AFQT requirements as the Coast Guard, has indicated they will also align their minimum AFQT enlistment qualifying scores with the new ASVAB norms, but I have not yet seen anything official stating that this has yet been implemented. The Army, Navy and Marine Corps have indicated they will not align their reporting scores with the new norms at this time, which essentially raises their standards for recruiting, although those standards will continue to be slightly below the Coast Guard and Air Force.